Optically compensated varifocal lens assembly



0mm# @QQ 35o-423 SR F. G. BACK 3,294,471

OPTICALLY COMPENSATED VARIFOCAL LENS ASSEMBLY Dec. 27, 1966 Filed June5. 1963 Zmm (D Q W@ Q LL x g M l NQ w u) FIG. 2

N VE NTOR. /ZAM/e 5,40

United States Patent O 3,294,471 OPTICALLY COMPENSATED VARIFOCAL LENSASSEMBLY Frank G. Back, 55 Sea Cliff Ave., Glen Cove, N.Y. 11542 FiledJune 5, 1963, Ser. No. 285,726 1 Claim. (Cl. 350-194) This inventionrelates to varifocal lens structures and particularly to an opticallycompensated varifocal lens arrangement for use in television cameras.The invention has particular reference to the means for compensating forthe aberration generally introduced into such a lens when the focallength is changed.

Varifocal lenses are well known in the art and have been used for sometime in the field of television, motion picture photography, and forstill cameras. Some of the prior art lenses have been limited todisclosure of image shift compensation only and have considerableaberrations during the shift from one focal length to another.

Aberrational correction in an optically compensated varifocal system ismuch more dtiicult than in an ordinary lens because the image defectschange with the focal length but not proportionally to it. Someaberrations change in the same sense as the focal length, others changeIinversely. In addition, the power of each lixed and movable lens groupis determined yby the zoom compensation. The customary method ofcorrecting alberrations by changing one radius and restoring therequired -powers by changing another radius which contributes relativelylittle to this aberration can therefore not be used in opticallycompensated varifocal lens systems.

Accordingly, it is an object of the present invention to provide avarifocal lens for use with television cameras which avoids some of thedisadvantages and limitations of prior art lenses.

Another object of the invention is to increase the range of the focallength so that a larger accommodation of image magnifications isavailable.

Another object of the invention is to provide highly satisfactory colorcorrection, both lateral and longitudinal for all focal length settings.

A feature of the present invention is its use of an air lens associatedwith each cemented surface in the lens system.

Another feature of the present invention is its use of a relay tocompensate for the constant aberrational residues.

The invention consists of the construction, combination and -arrangementof parts, as herein illustrated, described and claimed.

In the accompanying drawings, forming a part hereof, is illustrated onecomplete embodiment of the invention and in which:

FIGURE 1 is a view in longitudinal section of a complete opticallycompensated embodiment of the present invention showing the movableelements in the forward or telephoto position. v

FIGURE 2 is a view similar to FIGURE 1 showing the movable elements inthe rear or wide `angle position.

Referring now to the drawings, the lens system includes a negative frontlens -behind Iwhich there is mounted an axially movable lens assembly11, generally known in the art as the variator. The variator includestwo spaced positive lenses 12 and 13. A fixed air space S2 of the orderof 0.25% of the maximum focal length of the whole system is providedbetween the variator lenses 12, 13, said lenses being disposed withtheir larger contributing powers facing the fixed air space S2. Thevariator lenses 12, 13, have an outer front surface R3,

an outer rear surface R6, an inner front surface R4, and.

lCe

an inner rear surface R5, said surfaces having a power ldistributionaccording to the following relationship; lthe sum of the absolute valueof the curvatures of said inner front and rear surfaces facing the ixedair space between the variator lenses being at least twice but not morethan live times the sum of the absolute value of the curvatures of saidouter front surface and said outer rear surface facing variable airspaces to fulfill the condition:

dit-tak( tariffa) where R3 and R8 are each substantially equal to 1.2%of the maximum focal length of the whole system. A lens or lens systemhereinafter referred to as a compensator 14 is coupled to the variatorby a mechanical coupling 15 well known in the varifocal lens art so thatthe two may be moved together to change the focal length of the lenssystem. The compensator 14 includes three lenses 16, 17 and 18. A fixedair space S6 is provided between the lenses 17 and 18 of the order of0.2% of the maximum focal length of the whole system. Between themovable lens groups 11 and 14, there is positioned a fixed lens assembly20 which is generally known as the erector. The erector includes threelenses 21, 22 and 23. A fixed air space S4 is provided ybetween lenses22 and 23 of the order of 0.6% of the maximum focal length. The firstand second erector lens elements have an outer front surface R, facingthe variable air space S3 between the variator and erector, and au outerrear surface R11 facing the variable air space S5 between the erectorand compensator, an inner front surface R9, and an inner rear surfaceR10, both facing the fixed air space S4 between the erector elements,22, 23, said surfaces having a power distribution according to thefollowing relationship: the sum of the absolute values of the cur-Vatures of said inner front and rear surfaces facing the air space S4,being at least ll/z times lbut not more than 2.0 times the sum of theabsolute values of the curvatures of said outer front surface facing thevariable air space toward the variator and the outer rear surfacel thevariable air space opposite the compensator to fulfill the condition:

il a a 1 2 iR1 +R11 R9+iR1o 2 R1 +Rir where the absolute value of R9 isat least 1% but not more than 1% times the maximum focal length of theYwhole system and the absolute value R10 is at least 1A position of thefocal length of the entire system. Generally relays have had theirstrong negative components enclosed by one or more positive components.However, for the purpose of the present invention, it has been foundnecessary to provide a relay combination which consists of only onepositive lens followed Iby three negative lenses.

The lens assembly shown in FIGURES 1 and 2 consists of a negative frontlens 10, the front surface R1 of which has a radius of curvature atleast three times the maximum focal length of the whole system, and therear surface R2 having a radius of curvature at least equal to V2 themaximum focal length of the whole system, a

positive variator lens group 11, a negative erector lens 3 group 20, anda positive compensator lens group 14 followed by a diaphragm stop and apositi-ve relay 25. In order to achieve four point image shiftcompensation with equally spaced points of full compensation and minimumneeded. In order to obtain both the color correction and correction ofmonochromatic aberrations, an air lens is associated with each cementedsurface. The rst of these is the air lens formed by surfaces R14 and R15having an axial thickness of S6. The second air lens lies between zoomdeviation, the -powers of the variator 11 and com- 5 f R d R d h h. k fs ,pensator V14, are substantially equal while the absolute surtals b9auf() l agg ttlvug tbm Diss O1 4' (o value of the power of the erector20 is about twice that b s lien Wfl h a e efs l erm lona Cqrrec L In ofthe compensator 14 can I o ac ieved 1 t e power o t e erector 20 is equaI th 1 h th t h f ly distributed between the cemented and uncementedcom- 7n25 examp e s gwn, e varia or as a power O ponents and if theradius of curvature R7 of the front sur- 'lf lopters am? t e Compensatora Vflue of t'7'75 10 face is more than 0.5 but less than equal to theradius of dloptel's- The stationary erector 20 Positioned betweencurvature R11 of the `rear surface. Also, the curvatures the movablevariator 11 and compensator 14 has a power R9 and R10 enclosing thefixed air lens should have a of t4-125 dloPtefs- The Power of the frontlens 10 ratio of more than 1.00 but less than 2.00. These relaand thepower of the relay 25 have no influence on the 15 tionships can bewritten: zoom range nor the zoom deviation but does of course, determinethe focal length. This fact is well known in 1/2 lR7/R11l 1 the art andis fully explained in United States and Foreign 1 !R9/R10[ 2 Patents.

In a varifocal lens, since the image defects change with 20 The lXed elflens ln the efeCtoI (between lenses 22, 23) the focal length but notproportionally to it, some aberhas negative PoWer and ls substantiallyequal tothe Power rations change directly as the focal length changes,other of the tWo erector eonlponents- 1n the Compensator asaberrationschange inversely; that is, a decrease in focal sembly 14 the cementeddoublet 16, 17, haS about onelength produces an increase in aberrationsHOW these fourth of the power of the single element 18. The poweraberrations change depends upon the design of the lens 25 0f the all'lens 'between lenses 17 and 18 and having a system, whether the movableand xed components are radii of Cln'Vatnf es of R14 and R15, liesbetween the Powers positive or negative and whether or not theiraberrations of the enclosing glass lenses and ls PostlVe- The ratto ofare positive or negative. Also, the power of each fixed tbe tWo radiiR14 to R15, iS more than 8-0 but lesS than and movable lens group isdetermined by zoom com- 100 These l'elatlonshlps may be Written:

. 3o peUSatIOIl.. l The basic correction for a varifocal lens must bedirected to the reduction of longitudinal and lateral color defects.Where t 1s the Power m dlopters In the ,present invention this 1s doneby introducing two 8 IR1 4/R15l 10 0 cemented surfaces, one surface R13between movable lenses 35 16 and 17 and the other surface R3 between xedlenses Also, 1n tbe Compensator group 14, the ratio 0f the 21 and 22Each of these combinations includes two front radius of curvature R12 tothe rear radius of curvaglasses having the same refractive index butdifferent distur e R161s more than tWo but leSS than 3- persions. Achange of the radius of curvature of the 2 1R /R 3 cemented surface hasno effect on the focal length but 40 12 15K does change the colordefects. This compensation means The following table gives the opticalcharacteristics of is known in the art but other corrective effects arealso the system shown in the drawing and described above:

Lens N o. Radius R Thickness (t) Glass Cat. Index of Dispersion (in mm.)Air Spacing (s) Rel. Rei., ND V Front Lens:

R1=1474.665 1o t1=8.4 SFS-4 1. 7408 28.15

@F8014 Variator:

R1=552.181 12 1,=10.0 sK-ie 1. 62081 00. 4

82=1.0 R1=120.929 13 t=11.0 SK-i 1. 62081 60. 4

s.=115.671 Erector:

R1=-154.410 21 ti=3.0 LAK-10 1. 72062 50. 3

R,=39.970 22 ti=10.5 SF-ls 1. 72127 29. 3

,!|=2.9 Rip-187.939 23 t=4.12 LAK-10 1. 72062 50. 3

S5=6.085 Compensator:

R1,=459.78 1s 11= 12.68 SK-l 1. 62081 60. 4

R13=44.549 17---.. ti=2.50 F-2 1. 62081 36. 2

IMF-2252.556

I 85=1.0 R15=244.899 18 ia=5.5 SK-l 1 62081 60.4

IMF-107.83

1:11248 Stop See notes at end of table.

In the above table the symbols designate the following' ND equalsRefractive index for sodium D lines. V equals Abb's dispersion number.SFS equals Special Dense Flint (Shott Glassi. SK equals Dense Crown.

The focal length of the lens combination can be `varied from a maximumvalue of 470.50 mm. as shown in FIG- URE 1 to a minimum value of 78.40mm. thereby produc- F equals Flint.

LAK equals Lanthanum Crown. SF equals Dense Flint.

13K equals Borosilicate Crown.

the following order wherein ND is the refractive index for the D line, Vis Abbs dispersion number, SFS stands for Special Dense Flint, SKindicates Dense Crown, LaK

o ing a range of six to one. The yback focal length 1s O stands forLanthanum Crown, SF stands for Dense Flint, 100.70 mm. The movablelenses travel 102 mm. lfrom F indicates Flint and BK stands forBorosilicate Crown, the maximum to minimum value. R1 to R23 are therespective radii of refracting lens sur- Having thus fully described theinvention, what is faces numbered from front to rear of the lens systemtl claimed as new and desired to be secured by Letters Patent 2 to tlgare the respective axial thicknesses and .s1-sw are ofthe United States,is: D the respective separations from the front to the rear of Avarifocal lens system for television cameras cornthe lens system:

we rez-.1w e u?. Lens No, Radius R F rlfhickness (t) Glass Cat. Index ofDispersion (in mm.) Air Spacing (s) Ret. Rei., ND V Front Lens:

11F-1474.065 4 1o t =B. SFS-4 1. "408 R=26s l 28 15 81=S.914 Variator:

Ra=552.181 1.2 t=10.0 SK-16 1.62 1

rap-294.349 2 08 60 4 82=1.0 R5=120.929 13 7,=11.0 SK-16 1. 62081 60. 4

s3=115.671 Erector:

, 11F-154.410 21 t4=3.0 LAK-10 1. 72062 50. 3

R5=39.970 22 t5=10.5 SF-ls 1. 72127 29. 3

34=.9 Rip-187.939 23 156:4.12 LAK-10 1. 72062 5o. 3

85:6.085 Compensator:

R12=45a7s 16 t1=1268 SK-16 1. 62081 60. 4

lap-44.549 17 t=2.5o F-2 1. 62081 36. 2

8e=1.0 R15=44s99 1sti=5.6 SK-16 1. 62081 60. 4

Rip-167.83

s7=112.43 Stop Xg=5.0 Relay:

26 RFgm t so B Rip-102.34 6&5 27... m=3.0 F-2 1. 620s 36.2

89=4.25 rs IMF-SL65 i 4 o sF 72 2 z= -18 1. 127

m=18.5 30 R2z=149-69 t 28 S Equivalent focal length of the Wholes7ystem-(EFL)== 78,40 to 470.571

Back focal length of whole system=100. Radius, thickness and spacing inmillimeters.

prising, in the order of the direction of the incident light, 70 a frontlens, a front section of variable focal length including an axiallyslidable air spaced vnriator and compensator, a stationary erectortherebetween, an aperture stop spaced from the front section, and a rearsection of fixed focal length including a relay having three elementstherein said lens system having optical characteristics of ReferencesCited by the Examiner UNITED STATES PATENTS 3,011,403 12/1961 Dlutzik88-57 JEWELL H. PEDERSEN, Primary Examiner. R. I. STERN, AssistantExaminer.

